Mapping of hypothalamic sites involved in the effects of NPY on body temperature and food intake

The objective of the present study was to identify hypothalamic sites that might be implicated in the effects of neuropeptide Y (NPY) on both body temperature and food intake. For this purpose, the effects of direct microinjections of NPY in several doses (0.156–20 μg) into discrete hypothalamic nuclei on body temperature were examined in rats. To examine specificity of effects, food consumption of animals following injections was also measured. Results indicate that the influence of NPY on body temperature varies with the hypothalamic region where the peptide is administered. NPY had no effect on temperature after administration into the ventromedial (VMH) and the perifornical hypothalamus (PeF). However, a significant hypothermia was seen following administration into the preoptic (POA) and arcuate nucleus (Arc), and hyperthermia was seen after injection into the paraventricular nucleus (PVN). Finally, a biphasic effect was observed after injection into the lateral hypothalamus (LH): hyperthermia with relatively small doses and hypothermia with higher doses. Similar effects were obtained when administred into the third ventricle (3V) but in an inverted dose-related fashion: hypothermia at low and hyperthermia at higher doses. For feeding, NPY consistently increased food intake in all regions examined, with the strongest effect obtained after administration into the PeF. The present results clearly dissociate the effects of NPY on food intake and body temperature, and demonstrate that these effects are related to specific hypothalamic nuclei.     

Effects of centrally administered neuropeptide Y (NPY) and NPY13–36 on the brain monoaminergic systems of the rat

Summary The effects of centrally administered NPY on the brain monoamine systems were investigated in the rat. Neuropeptide Y (0.2–5.0 nmol), its C-terminal 13–36 amino acid (a.a.) fragment, NPY_13–36 (0.4–10.0 nmol), or saline were injected into the right lateral cerebral ventricle of unrestrained rats. After l h the animals were decapitated, and the brains were taken out. Two cortical regions (frontal and parietal), the striatum, the hypothalamus, and the brain stem were dissected out. The tissue contents of noradrenaline (NA), dopamine (DA) and serotonin (5-HT), as well as of their major metabolites, 3-methoxy-4-hydroxy-phenylethylené glycol (MHPG), 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxy-indole acetic acid (5-HIAA) were measured. The most consistent finding was a dose-related increase of both DA and DOPAC levels after treatment with NPY. This effect was reproduced by NPY_13–36 in cortical tissue, whereas, in the sub-cortical regions, NPY_13–36 only reproduced the effects of NPY on the DOPAC levels. Less consistent effects were found on the NA systems, in which NA levels showed a tendency to increase following low, and decrease after high doses of NPY. These effects were largely reproduced by NPY_13–36. In addition, NPY increased tissue levels of MHPG in frontal cortical tissue in a dose-related manner. The brain 5-HT systems were not affected.     

Anorexic action of a new potential neuropeptide Y antagonist [ -Tyr, -Thr]-NPY (27–36) infused into the hypothalamus of the rat

Neuropeptide Y (NPY) produces a vigorous feeding response in several species when it is injected into hypothalamic structures involved in eating behavior. The purpose of this study was to determine whether a unique carboxy terminal fragment of NPY would alter the pattern of eating induced in the rat either by NPY injected into the hypothalamus or by a 24-h period of food deprivation. In this case, two -tyrosine residues and one t.-threonine residue of the NPY_27–36 fragment were transformed to their D-conformation to produce [ -Tyr^27,36, -Thr³²]-NPY (27–36), i.e., D-NPY_27–36. Guide cannulae for microinjection were implanted stereotaxically just dorsal to the paraventricular nucleus (PVN) or ventromedial hypothalamus (VMH) of 24 adult male Sprague-Dawley rats. Following postoperative recovery, a microinjection of artificial CSF or 1.1 jig or 3.3 μg of a peptide was made directly into the PVN or VMH as follows; native NPY; D-NPY_27–36; or [L-Tyr^27,36 L-Thr³²]-NPY (27–36), i.e., L-NPY_27–36. Food intakes were measured at intervals of 0.25, 0.5, 1.1, 2.0, 4.0, and 24 h. When D-NPY_27–36 was microinjected at NPY reactive sites in the PVN or VMH of the rat 15 min before a similar microinjection of NPY, the intense eating response induced by the peptide was reduced significantly. Not only was the effect dose dependent, but D-NPY_27–36 also augmented the latency to feed. A mixture of the two doses of NPY and DNPY_27–36 injected at the same hypothalamic loci did not attenuate the intake of food but tended to enhance the feeding response in the rats. After the rats were deprived of food for 24 h, D-NPY_27–36 microinjected in the same hypothalamic sites similarly caused a dose-dependent suppression of normal feeding behavior. However, the CSF control vehicle and L-NPY_27–36 microinjected in the PVN or VMH were without effect on the pattern of eating. Further, D-NPY_27–38 injected in the same hypothalamic sites affected neither body temperature nor water intakes of the rats significantly. These results demonstrate that the D substitution of this C-fragment of the NPY molecule, i.e., D-NPY_27–36, serves to inhibit feeding evoked in the rat by hypothalamic NPY as well as the natural eating response to food deprivation. Thus, the D-NPY_27–36 molecule may act as an antagonist at one or more subtypes of the NPY receptor in the brain of the rat.     

Regulation of proopiomelanocortin gene expression by neuropeptide Y in the rat arcuate nucleus

In the arcuate nucleus which is richly innervated by both proopiomelanocortin (POMC) and neuropeptide Y (NPY) neurons, it has been shown that NPY fibers are in synaptic contact with POMC cell bodies. In order to determine whether NPY could influence POMC neuronal activity, we have studied the effects of NPY and some NPY analogs on POMC gene expression using quantitative in situ hybridization. The following peptides NPY, [Leu³¹, Pro³⁴]-NPY (a Y₁ receptor agonist), and NPY_13–36 (a Y₂ receptor agonist) were injected into the left lateral cerebral ventricle of adult male rats 4 h before being perfused for histological procedures. The intracerebroventricular injection of NPY and NPY_13–36 induced a significant decrease in the number of grains overlying the labelled neurons. On the other hand, the Y₁ receptor agonist [Leu31, Pro34]-NPY did not modify POMC mRNA levels. These data then strongly suggest that NPY negatively regulates the genetic expression of POMC neurons via the Y₂ NPY receptor subtype.     

Anxiolytic-like effect of neuropeptide Y (NPY) and NPY13–36 microinjected into vicinity of locus coeruleus in rats

Neuropeptide Y (NPY, 1 and 10 pmol), NPY Y₁ receptor agonist [Leu³¹,Pro³⁴]NPY (10 pmol) and Y₂ agonist NPY_13–36 (100 pmol) were administered unilaterally into the region of the nucleus locus coeruleus (LC) in rats. NPY (10 pmol) and NPY_13–36 increased the percentage of open arm entries, the percentage of time spent on open part, number of both open and closed arm entries and line crossings in the open part while [Leu³¹,Pro³⁴]NPY failed to modify elevated plus-maze behavior. These data suggest that NPY applied close to LC has anxiolytic-like effects by acting on NPY Y₂, not on Y₁ receptors. Thus, NPY Y₂ receptors in the vicinity of LC may be involved in the regulation of anxiety in rats.     

[Leu,Pro]Neuropeptide Y (NPY), but not NPY 20–36, produces discriminative stimulus effects similar to NPY and induces food intake

Rats were trained to discriminate between an intracerebroventricular injection of 1.15 nmol of Neuropeptide Y (NPY) and a sham injection. Rats rapidly learned to press the appropriate lever during training. NPY's discriminative stimulus effects were compared to those of saline, and 1.15–3.45 nmol [Leu³¹,Pro³⁴]NPY, a Y₁ receptor agonist and NPY 20–36, Y₂ receptor agonist. [Leu³¹,Pro³⁴]NPY resulted in NPY-appropriate responding, whereas saline and NPY 20–36 did not. [Leu³¹,Pro³⁴]NPY also increased food intake, but NPY 20–36 did not. This suggests that NPY's discriminative stimulus and orexigenic effects involve the Y₁, but not the Y₂, receptor.     

Anorexic action of a new potential neuropeptide Y antagonist [d-Tyr, d-Thr]-NPY (27–36) infused into the hypothalamus of the rat

Neuropeptide Y (NPY) produces a vigorous feeding response in several species when it is injected into hypothalamic structures involved in eating behavior. The purpose of this study was to determine whether a unique carboxy terminal fragment of NPY would alter the pattern of eating induced in the rat either by NPY injected into the hypothalamus or by a 24-h period of food deprivation. In this case, two l-tyrosine residues and one t.-threonine residue of the NPY_27–36 fragment were transformed to their D-conformation to produce [d-Tyr^27,36,d-Thr³²]-NPY (27–36), i.e., D-NPY_27–36. Guide cannulae for microinjection were implanted stereotaxically just dorsal to the paraventricular nucleus (PVN) or ventromedial hypothalamus (VMH) of 24 adult male Sprague-Dawley rats. Following postoperative recovery, a microinjection of artificial CSF or 1.1 jig or 3.3 μg of a peptide was made directly into the PVN or VMH as follows; native NPY; D-NPY_27–36; or [L-Tyr^27,36 L-Thr³²]-NPY (27–36), i.e., L-NPY_27–36. Food intakes were measured at intervals of 0.25, 0.5, 1.1, 2.0, 4.0, and 24 h. When D-NPY_27–36 was microinjected at NPY reactive sites in the PVN or VMH of the rat 15 min before a similar microinjection of NPY, the intense eating response induced by the peptide was reduced significantly. Not only was the effect dose dependent, but D-NPY_27–36 also augmented the latency to feed. A mixture of the two doses of NPY and DNPY_27–36 injected at the same hypothalamic loci did not attenuate the intake of food but tended to enhance the feeding response in the rats. After the rats were deprived of food for 24 h, D-NPY_27–36 microinjected in the same hypothalamic sites similarly caused a dose-dependent suppression of normal feeding behavior. However, the CSF control vehicle and L-NPY_27–36 microinjected in the PVN or VMH were without effect on the pattern of eating. Further, D-NPY_27–38 injected in the same hypothalamic sites affected neither body temperature nor water intakes of the rats significantly. These results demonstrate that the D substitution of this C-fragment of the NPY molecule, i.e., D-NPY_27–36, serves to inhibit feeding evoked in the rat by hypothalamic NPY as well as the natural eating response to food deprivation. Thus, the D-NPY_27–36 molecule may act as an antagonist at one or more subtypes of the NPY receptor in the brain of the rat.     

Central injection of a σ opioid receptor agonist alters body temperature of cats

The prototype σ opioid receptor agonist Nallyl-normetazocine (SKF 10,047) was injected into the third cerebral ventricle of conscious, unrestrained cats, and their temperature was monitored automatically from the retroperitoneal space. In a cold environment (0°C) a small, but not dose-related, hypothermia occurred after doses of 100–500 μg. This response was not antagonized by naloxone given intraventricularly either 15 min before or 1 hr after the opioid. A smaller hypothermia resulted after 250 μg SKF 10,047 when the environmental temperature was 22°C, whereas hyperthermia developed in a hot environment (34°C). Thus SKF 10,047 appears to allow body temperature to drift, upward in the heat and downward in the cold, a pattern indicative of thermoregulatory depression. These results are similar to those obtained in the first 2–3 hr after pentazocine administration, and they support a previous classification of the initial temperature response to centrally injected pentazocine as due to stimulation of σ opioid receptors.     

Intracerebroventricular neuropeptide Y increases gastric acid secretion by decreasing tonic adrenergic inhibition of acid in dogs

Neuropeptide Y (NPY) has been shown to increase basal gastric acid secretion in dogs. We examined the hypothesis that NPY might increase gastric acid secretion by interaction with central catecholaminergic control of acid secretion in dogs. Studies were performed in awake canines with gastric fistulas and cerebroventricular guides which allowed injection into the lateral cerebral ventricle. Intracerebroventricular (i.c.v.) injection of yohimbine (5 μg/kg) increased acid secretion compared to control (yohimbine: 9.1 ± 3.3mmol//h;control: 1.8 ± 1.0mmol/2h, P < 0.05), whereas prazosin and propranolol (both 5 μg/kg i.c.v.) had no effect, suggesting that there is tonic central α₂-adrenergic inhibition of acid secretion. NPY_13–36 significantly increased acid secretion compared to control (NPY_13–36 1000pmol/kg i.c.v.: 5.6 ± 1.9mmol/2h;control: 1.3 ± 0.8mmol/2h, P < 0.05), whereas [Leu³¹, Pro³⁴]-NPY had no effect, suggesting that the central effect of NPY is mediated at a Y₂, probably pre-synaptic receptor. Finally, i.c.v. desmethylimipramine (DMI) inhibited the acid response to i.c.v. NPY when injected before but not after NPY (i.c.v. DMI then i.c.v. NPY: control,15.2 ± 6.6mmol/2h;DMI, 3.5 ± 1.2mmol/2h, P< 0.05; i.c.v. NPY followed by i.c.v. DMI: control,8.9 ± 4.0mmol/2h;DMI, 9.9 ± 2.9mmol/2h, P > 0.05). This suggests that NPY acts by decreasing noradrenaline release. These findings are compatible with the hypothesis that i.c.v. NPY increases acid secretion by decreasing tonic central adrenergic inhibition of acid by decreasing release of noradrenaline at pre-synaptic level.     

Hyperthermic response of the cat to intraventricular injection of the opioid delta-receptor agonist D-AlaD-Leuenkephalin

The δ opioid receptor agonist D-Ala²-D-Leu⁵-enkephalin was injected into the third cerebral ventricle of cats to determine its effects on core temperature for comparison with other peptide and non-peptide opioids that act on a variety of receptors to alter thermoregulation. Like other opioid peptides that have been studied in this species, D-Ala²-D-Leu⁵-enkephalin (5–25 μg) induced a dose-related hyperthermia. This response was undiminished in cats tolerant to morphine and was found to consist of two components. One component of the hyperthermic response was inhibited by pretreatment with low doses of opioid antagonists (25μg naloxone; 5–15μg naltrexone) and may be mediated by the v₂-receptor that mediates this response to D-Ala²-Met-enkephalinamide. The other component, which was prevented by 100μg naltrexone but still only partially inhibited by 250 μ naloxone, is attributed to δ-receptor stimulation. In tests over a range of environmental temperatures, the hyperthermic response to 10μg D-Ala²-D-Leu⁵-enkephalin was less in a 4°C environment than at the usual laboratory temperature of 22°C. Responses in 22 and 34°C environments were similar. No increase in respiratory rate occurred to indicate activation of compensatory heat-loss mechanisms so that the hyperthermia was indicative of an increase in the level about which body temperature is regulated.     

Role of Neuropeptide Y in the Regulation of Tyrosine Hydroxylase Messenger Ribonucleic Acid Levels in the Male Rat Arcuate Nucleus as Evaluated by in situ Hybridization

Neuroanatomical data have clearly demonstrated the existence of synaptic contacts between neuropeptide Y (NPY) endings and tuberoinfundibular dopaminergic (TIDA) neurons in the rat arcuate nucleus. In order to determine the influence of NPY in the biosynthesis of dopamine, we have studied the effects of NPY and some NPY analogs on tyrosine hydroxylase (TH) gene expression in TlDA neurons in the male rat. The following peptides: NPY, PYY, [Leu³¹, Pro³⁴]-NPY (a Y, receptor agonist) and NPY_13–36 (a Y₂ receptor agonist) were injected into the left lateral ventricle of adult male rats. All the animals were perfused with 4% paraformaldehyde 4 h after injection. Cryostat sections through the arcuate nucleus were processed for quantitative in situ hybridization. The intracerebroventricular injection of NPY, PYY and [Leu³¹, Pro³⁴]-NPY induced an increased of 43, 33 and 42%, respectively, in the number of grains overlying TH neurons. On the other hand, the Y₂ receptor agonist NPY_13–36 did not influence mRNA levels. These data then strongly suggest that NPY positively regulates the genetic expression of TH in rat TlDA neurons via the Y, NPY receptor subtype.     

Weight loss in rats treated with intracerebroventricular cobalt protoporphyrin is not specific to the neuropeptide Y system

Cobalt protoporphyrin (CoPP) reduces food intake and body weight following intracerebroventricular (i.c.v.) administration in rats. We injected 0.2 μmol CoPP per kg body weight i.c.v. and monitored body weight and daily food intake for 7 days. The body weight and 24 h food intake of CoPP-treated animals was significantly lower than that of vehicle-treated animals in all studies (P < 0.01) from day 2 to day 7. The 2 h feeding response (CoPP vs. vehicle-treated) to 10 μg neuropeptide Y (NPY) (4.0 vs. 7.1 g;P < 0.05), the 1 h feeding response to 10 μg galanin (1.3 vs. 3.2 g;P < 0.05) and 30 μg norepinephrine (0.6 vs. 1.9 g;P < 0.05) in CoPP-treated animals were all reduced compared to the vehicle-treated group. In addition there was no change in hypothalamic NPY mRNA in CoPP-treated animals. I.c.v. COP decreases sensitivity to exogenous NPY, galanin and norepinephrine. The effect of COP is not specific to NPY as previously described.     

The effect of intrathecal selective agonists of Y1 and Y2 neuropeptide Y receptors on the flexor reflex in normal and axotomized rats

We have examined the effects of intrathecal (i.t.) administration of [Leu³¹,Pro³⁴]-neuropeptide Y (NPY) or NPY-(13–36), selective agonists of NPY Y₁ or Y₂ receptors, respectively, on the excitability of the flexor reflex in normal rats and after unilateral transection of the sciatic nerve. In rats with intact and sectioned sciatic nerves, i.t. [Leu³¹,Pro³⁴]-NPY induced a similar biphasic effect on the flexor reflex with facilitation at low doses and facilitation followed by depression at high doses. In contrast, i.t. NPY-(13–36) only facilitated the flexor reflex in normal rats, and at high dose it caused ongoing discharges in the electromyogram. NPY-(13–36) caused dose-dependent depression of the flexor reflex in rats after sciatic nerve transection, in addition to its facilitatory effect. Topical application of [Leu³¹,Pro³⁴]-NPY or NPY-(13–36) caused a moderate and brief reduction in spinal cord blood flow. No difference was noted between the vasoconstrictive effect of [Leu³¹,Pro³⁴]-NPY and NPY-(13–36). It is suggested that activation of Y₁ receptors may be primarily responsible for the reflex depressive effect of i.t. neuropeptide Y in rats with intact sciatic nerves, whereas both Y₁ and Y₂ receptors may be involved in mediating the depressive effect of NPY after axotomy.     

In vivo structure activity study supports the existence of heterogeneous neuropeptide Y receptors

The purpose of the present study was to examine relationships between structure and activity of the peptide for stimulating food intake and decreasing body temperature in rats. Various NPY fragments and structural analogs were administered intracerebroventricularly in several doses (2.5-160 micrograms) and their effects on feeding and body temperature evaluated and compared. Globally, results indicate that the C-terminal portion of the peptide is responsible for both central effects of NPY. However, the distributions of potencies of the various fragments and analogs for increasing food intake and decreasing body temperature were clearly different. The most salient difference was that deletion of the N-terminal residue Tyr1 of NPY resulted in a five-fold loss in the potency for decreasing rectal temperature, whereas NPY2-36 was relatively more potent than the native peptide to increase food intake in animals. These results suggest that the purported receptors mediating the effect of NPY on food intake are different than those responsible for the influence of the peptide on body temperature. The results of the present in vivo work are discussed in relation to those obtained in previous in vitro studies.     

Activation of neuropeptide Y(2) receptors exerts an excitatory action on cardio-respiratory variables in anaesthetized rats

The respiratory effects of stimulation of NPYY₂ receptors were studied in spontaneously breathing rats that were either (i) neurally intact and subsequently bilaterally vagotomized in the neck, or (ii) neurally intact and subjected to supranodosal vagotomy or (iii) neurally intact treated with pharmacological blockade of NPY_1-2 receptors. Before neural interventions an intravenous (iv) bolus of the NPYY₂ receptor agonist NPY 13-36 (10 μg/kg) increased breathing rate, tidal volume and mean arterial blood pressure (MAP).Section of the midcervical vagi abrogated NPY 13-36-evoked increase in respiratory rate but had no effect on augmented tidal volume, minute ventilation and blood pressure. Supranodosal vagotomy prevented the increase in tidal volume and slightly reduced the pressor response. Blockade of NPYY₂ receptor with intravenous doses of BIIE 0246 eliminated cardio-respiratory effects of NPY 13-36 injection. BMS 193885 - an antagonist of NPYY₁ receptor-was not effective in abrogating cardio-respiratory response.The present study showed that (i) NPY 13-36 induced stimulation of breathing results from activation of NPYY₂ receptors associated with pulmonary vagal afferentation; (ii) the increase in the frequency of breathing is mediated by midcervical vagi and augmentation of tidal volume relies on the intact supranodosal trunks (iii) the pressor response results from the excitation of NPYY₂ receptors outside of the vagal pathway.     

Neurobehavioral profile of neuropeptide Y

In order to better delineate the profile of central actions of neuropeptide Y (NPY), the effects of intracerebroventricular administration of several doses (2.5-20 micrograms) of the peptide on spontaneous activity, muscular tone, body temperature, food intake, nociception and cataleptic manifestations were examined in rats. Results indicate that, starting at 5 micrograms. NPY significantly decreased motor activity of animals in a dose-related fashion. NPY also significantly lowered body temperature of animals. The hypothermic effect was obtained following injections of 10.0 and 20.0 micrograms of the peptide. Administration of the same two doses of NPY resulted in significant increases in food intake, muscular tone and induced a significant catalepsy in animals. On the other hand, nociceptive response times of animals in the hot plate test were not affected by any of the NPY doses tested. Together, these results indicate that the profile of NPY's neurobehavioral actions is more complex than previously reported and suggest that the peptide might be implicated functionally in a variety of neurophysiological processes.     

Influence of fasting and neuropeptide Y on the suppressive food intake induced by intracerebroventricular injection of glucagon-like peptide-1 in the neonatal chick

Recently, we have reported that central administration of glucagon-like peptide-1 (GLP-1) strongly decreased food intake of chicks. The aim of the present study was to elucidate whether suppressed food intake by central injection of GLP-1 would be modified by an appetite stimulant such as fasting and neuropeptide Y (NPY). Birds (2 days old) were starved for 3 or 6 h and then GLP-1 (0.03 μg/10 μl) or saline was injected by the intracerebroventricular (i.c.v.) route. Birds starved for 6 h ate significantly more food than those starved for 3 h, while irrespective of the time for fasting GLP-1 strongly inhibited food intake as rapidly as 10 min after i.c.v injection. The suppressive effect on food intake continued until 4 h after injection. Central administration of NPY (2.5 μg/10 μl) greatly enhanced food intake, but co-injection of GLP-1 (0.01, 0.02 or 0.03 μg/10 μl) decreased food intake in a dose-dependent fashion. Under GLP-1 (0.03 μg/10 μl) treatment, whether NPY modifies food intake of chicks in a dose-dependent manner was investigated by co-injection of graded levels of NPY (0.4, 1.0 and 2.5 μg/10 μl). GLP-1 completely inhibited the effect of NPY on food intake without a dose response. These results suggest that central GLP-1 may interact with NPY and may be the most potent inhibitor of food intake in the chicken.     

Neuropeptide Y induces torpor-like hypothermia in Siberian hamsters

Intracerebroventricular (ICV) injections of neuropeptide Y (NPY) are known to decrease body temperature (Tb) of laboratory rats by 1-3 degrees C. Several NPY pathways in the brain terminate in hypothalamic structures involved in energy balance and thermoregulation. Laboratory rats are homeothermic, maintaining Tb within a narrow range. We examined the effect of ICV injected NPY on Tb in the heterothermic Siberian hamster (Phodopus sungorus), a species that naturally undergoes daily torpor in which Tb decreases by as much as 15-20 degrees C. Minimum effective dose was determined in preliminary testing then various doses of NPY were tested in cold-acclimated Siberian hamsters while food was withheld. NPY markedly reduced Tb in the heterothermic Siberian hamster. In addition, the reduction in Tb in 63% of the observations was sufficient to reach the criterion for daily torpor (Tb < 32 degrees C for at least 30 min). Neither the incidence of torpor nor its depth or duration was related to NPY dose. Both likelihood and magnitude of response varied within animals on different test days. NPY decreased 24-h food intake and this was exaggerated in the animals reaching criterion for torpor; the decrease in food intake was positively correlated with the magnitude of the decrease in Tb. The mild hypothermia seen in homeothermic laboratory rats after NPY injected ICV is exaggerated, often greatly, in the heterothermic Siberian hamster. NPY treatment may be activating hypothalamic systems that normally integrate endogenous torpor-producing signals and initiate torpor.     

Lack of NPY in neurotensin neurons leads to a lean phenotype

Neuropeptide Y (NPY) producing neurons in the arcuate nucleus (Arc) of the hypothalamus are essential to the regulation of food intake and energy homeostasis. Whilst they have classically been thought to co-express agouti-related peptide (AgRP), it is now clear that there is a sub-population of NPY neurons in the Arc that do not. Here, we show that a subset of AgRP-negative, NPY-positive neurons in the Arc also express neurotensin (NTS) and we use an NTS-Cre line to investigate the function of this sub-population of NPY neurons. The lack of NPY in NTS-positive neurons led to a marked reduction in fat mass and bodyweight as well as a significant reduction in food intake in male NPY^lox/lox; NTS^cre/+ mice compared to controls. Despite the reduction in food intake, overall energy expenditure was similar between genotypes due to concomitant reduction in activity in NPY^lox/lox; NTS^cre/+ mice. Furthermore, cortical bone mass was significantly reduced in NPY^lox/lox;NTS^cre/+ mice with no evident alterations in the cancellous bone compartment, likely due to reduced leptin levels as a result of their reduced adiposity. Taken together, these data suggest that the sub-population of Arc NPY neurons expressing NTS are critical for regulating food intake, activity and fat mass but are not directly involved in the control of bone mass.     

Effects of centrally administered pentazocine and ethylketocyclazocine on thermoregulation in the cat

The mechanisms for the biphasic response of unrestrained cats to centrally administered pentazocine were examined by injecting 1 mg pentazocine into the third cerebral ventricle at various ambient temperatures (T_as). The initial phase was hyperthermia at T_a = 34°C, but at T_a = 22°C hypothermia, which was enhanced at T_a = 0°C, developed. The second phase was an increase in body temperature that occurred at all three T_as. No evidence was seen of compensatory thermoregulatory effector activity during development of either phase. The first phase can be attributed to general depression of thermoregulation whereas the second phase was likely due to an increase in the level about which body temperature was regulated. Ethylketocyclazocine (250–1000 μg) caused a very similar, dose-related change in temperature, neither phase of which, as reported previously for pentazocine, was reduced by a large dose of naloxone. Thus both agonists appear to act on the same receptors to alter thermorégulation in the cat. These receptors are distinct from the naloxone-sensitive receptors stimulated by morphine.